Douglas Krantz - Technical Writer - Describing How It Works
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What is Smoke Detector Verification?

Popcorn being prepared can send a breif wif of smoke, which sets off the smoke detector. Verification in a fire alarm system makes sure the smoke is lasting more than a few short seconds before sounding the alarms.
Preparing popcorn sometimes produces brief smoke. Being skeptical, a fire alarm system verifies that smoke is long lasting before sounding the alarms.


By Douglas Krantz

Because smoke comes in so many varieties, smoke detectors have to be sensitive to anything that even looks like smoke. Not only that, but smoke detectors aren't smart; they really can't differentiate between smoke from a dangerous fire and dust that looks like smoke, steam that looks like smoke, or sometimes even Cajun cooking that looks like smoke.

One method of reducing false alarms is the use of verification. Without verification, a short-term detection of smoke from overcooked popcorn down the hall or soldering in the next room that quickly goes away will set off the alarms.

Verification gets past this by resetting the smoke detector after the first detection of smoke, and then, a short time later, checking for the smoke again.

It's the second detection of smoke, during this verification time, that sets off the alarms.

Skepticism

Another way of describing verification is that verification is the fire alarm panel's way of being skeptical.

A smoke detector panics and says "I smell smoke!"

Being skeptical that there really is smoke, the fire alarm panel says "Are you sure? Reset yourself and in 30 seconds try looking for the smoke".

For a total of 90 seconds from the first indication of smoke, the panel waits in a standby condition. If, during that standby, the smoke detector doesn't say it smells smoke, without going into alarm the panel returns to a normal condition.

Of course, if during that 90 seconds of standby, that smoke detector or even another smoke detector smells smoke, the fire alarm panel assumes there really is smoke because smoke has been detected twice, and the panel sounds the alarm.

So, using the skepticism of verification, the fire panel checks twice for smoke and can avoid many of the false alarms from a single, short-term, detection of smoke.
Based on his electronics training, and his understanding of Life Safety, Douglas Krantz has compiled his knowledge of Conventional Fire Alarm Systems into the book Make It Work - Conventional Fire Alarms. The book covers the basics of the Conventional Fire Alarm System, and shows how Life Safety and internal supervision affects the fire alarm system.

Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

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